The present invention relates to a remote steering system that is primarily intended for use with surgical catheters. However, the invention may also be employed in connection with medical implants, switchgear and certain industrial pipeline equipment.
Surgical catheterization provides a desirable and readily implementable procedure for accomplishing various diagnostic and therapeutic objectives in a manner which is relatively expedient and free of trauma to the patient. In typical catheterization procedures, a blood vessel adjacent to the surface of the skin of a patient is punctured to provide entry of the catheter into the blood vessel lumen. Once entry of the blood vessel has been accomplished, the catheter can be advanced through the patient's vascular system, typically with the aid of various radiographic imaging techniques, to a desired internal organ or tissue site. Advancement of the catheter in this manner typically requires traversing a variety of angled and curved paths. Since many conventional catheters have generally cylindrical, flexible tubular structures, passage of the catheter along the desired angled or curved paths is accomplished by sliding the catheter over a guidewire.
Depending on the particular catheterization procedure and the path along which the catheter is to be advanced, the catheter guidewire may need to be changed on a number of occasions during the course of the procedure. Such guidewire changeover can be both time consuming and inherently risky, as vasculature of various dimensions must be traversed, possibly giving rise to incidents of vascular trauma and even rupture. Blood vessel rupture can radically transform the medical procedure from one of relatively routine diagnostic study to an emergency invasive surgical procedure, thus jeopardizing the health and even the life of the patient. Due to the foregoing difficulties and risks, surgical catheterization has evolved into a surgical specialty in its own right.
Previous efforts to produce remotely steered catheters have focussed on the use of shape memory metal alloys in order to provide desired curvilinear configurations for the distal ends of the catheters, so as to avoid altogether the requirement for guidewires. Examples of catheters employing shape memory metal alloys are disclosed in U.S. Pat. Nos. 4,994,727 and 4,919,133. As explained in the background portion of the latter patent, shape memory alloys are capable of transforming from a first configuration to a second configuration upon reaching a predetermined threshold temperature. This transformability apparently arises as a result of the crystalline structure that is imposed on the metal as a result of the particular metal annealing regimen that is employed. However, because shape memory alloys are generally "dormant" with respect to transformability until their respective transformation temperatures have been attained, catheters formed from such materials are generally unsuited for all but the most simple catheterization procedures. These catheters are generally transformable only into predetermined specific configurations rather than the broad range of configurations that are typically required to advance the catheter to remote internal sites incident to the performance of more sophisticated diagnostic and therapeutic procedures. For at least the foregoing reasons, catheters formed from shape memory alloys have not gained widespread acceptance for surgical catheterization on human patients.